Examples of electrochemical devices in which organic solvent-containing electrolysis solutions (non-aqueous electrolysis solutions) are used include electric double-layer capacitors and lithium ion batteries. In such electrochemical devices, it is necessary to prevent evaporation and leakage of sealed-in electrolysis solution and also to prevent infiltration of water and water vapor from outside of the electrochemical device. For this reason, sealants are widely used in electrochemical devices.
Vinyl aromatic hydrocarbon-conjugated diene block polymers, hydrogenated products thereof, conjugated diene polymers, and so forth have been proposed as sealants (for example, refer to PTL 1). These sealants are suitable in a situation in which a gasket for battery sealing is formed from a polyolefin such as polypropylene that is a non-polar resin.
In recent years, applications for electrochemical devices have expanded to electric vehicles and the like, resulting in demand for durability at even higher temperatures. Consequently, thermoplastic polyester elastomers (TPCs), which are resins having high mechanical strength at high temperature and good flexibility at low temperature, are being used as materials of gaskets for battery sealing. Since TPCs are resins that have high polarity compared to polypropylene and the like, there are cases in which sufficient wettability and adequate close adherence cannot be obtained using sealants that do not include polar groups. In other words, when a sealant that does not include a polar group, such as a sealant designed for gaskets made from polypropylene, is used with respect to a gasket made from a TPC, sealing performance may be insufficient.